#include <stdio.h>

int main() {
    double score;
    scanf("%lf", &score);

    if (score >= 90 && score <= 100) {
        printf("A");
    } else if (score >= 80 && score < 90) {
        printf("B");
    } else if (score >= 70 && score < 80) {
        printf("C");
    } else if (score >= 60 && score < 70) {
        printf("D");
    } else if (score >= 0 && score < 60) {
        printf("E");
    } else {
        printf("ERR");
    }

    return 0;
}

